Explain why cells must replicate their DNA before mitosis can take place, and describe what happens to the chromosomes during anaphase.

Edexcel GCSE Biology (1BI0) — 2.1 Mitosis and the cell cycle · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

DNA must be replicated so that each daughter cell receives a complete set of genetic information; replication produces two identical chromatids for each chromosome, ensuring diploidy. Without replication, cells would end up with half the chromosome number.

During anaphase the sister chromatids are pulled apart by spindle fibres to opposite poles of the cell.

Examiner tips

  • Use the word ‘replicate’ and explain the diploid requirement; mention chromatids and spindle fibres in anaphase; keep answer concise and use correct terminology.
  • Show the logical link: replication → two chromatids → diploid daughter cells; anaphase → separation by spindle fibres.

Common mistakes

  • Failing to mention that replication produces two identical chromatids; saying chromosomes split without referencing spindle fibres; confusing anaphase with metaphase or telophase.

Mark scheme (4 marks)

  1. DNA replication produces two identical copies of each chromosome (chromatids) / ensures each daughter cell receives a full / complete set of genetic information
  2. Without DNA replication, daughter cells would have too few / half the number of chromosomes (they would not be diploid)
  3. During anaphase, the chromatids are pulled to opposite poles of the cell
  4. The chromatids are pulled by spindle fibres

Key terms in this question

anaphase

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